Acid inhibitor



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Patented July 2, 1935 UNITED STATES PATENT OFFICE ACID INHIBITOR DWilmington, Delaware Del.,

a corporation of No Drawing. Application February 23, 1932, Serial No. 59L8 50 Claims.

This invention relates to acid pickling solutions for metals and moreparticularly to pickling solutions containing substances for inhibitingthe solvent action of the acids on metals while permitting the acid toattack and remove corrosion and like products from the surfaces of themetal.

It is well known that iron, steel, nickel and like metals in use and onexposure to the elements and to certain chemicals become coated withscale, basic salts, and corrosion products such as rust and the like. Itis common to treat such metals to remove these objectionable matters byimmersing the metals in a pickling solution comprising a dilute aqueoussolution of a strong non-oxidizing acid. The acid attacks and dissolvesthe scale, basic salts, and corrosion products but at the same time hasa tendency to attack the base metal. It has, therefore, been proposed toincorporate into such pickling solutions a substance or substances whichwill inhibit the solvent action of the acid on the metal while at thesame time permitting the acid to dissolve and remove the objectionablematters. The substances employed for this purpose up to the present timehave not been entirely satisfactory for various reasons. For example,the inhibitors are not sufficiently soluble in dilute acid to enabletheir ready incorporation into the pickling solutions; some of themrequire complicated processes therefor; others have but very weakinhibiting action requiring the addition of large amounts thereof to thepickling solution; still others are very unstable in the acid used; andsome of the inhibitors can not be readily removed from the metal byrinsing with water but require the use of an organic solvent or thelike.

The present invention has as an object to provide substances to be addedto pickling solutions to inhibit the solvent action of acids on metalswhile permitting the removal of objectionable matters. Another object isto provide a class of acid inhibitors which are readily soluble indilute acid. A further object is to provide a class of acid inhibitorswhich may be readily washed from metal by rinsing with water. Stillfurther objects are to provide a new composition of matter and toadvance the art. Other objects will appear hereinafter.

These objects are accomplished by the following invention whichcomprises the preparation of a pickling solution by adding to a dilutesolution of a strong non-oxidizing acid the product or products whichmay be obtained nation of cert combination takes place under conditionssuch as do not permit the evolution of hydrogen sulfide. The amineemployed in accordance with our invention comprises a class of organicwines in which at leastgig'o'f thfanunq groups is and at least one ofthe other amino groups 1 s t'eTtiary. The'aldehyde and carbon disulfidemay be caused to combine with any single member of the class, a mixtureof two or more members of the class, or a mixture of one or more of suchpolyamines with an aromatic monoamine such as aniline. Such combinationproduces a compound or compounds which have very effective acidinhibiting properties when dissolved in a pickling bath of dilute acid.These compounds have the additional advantage of being readily solublein dilute acids and are also readily washed from the surface of themetal by water.

While the acid inhibitors forming the subject matter of this inventionmay be prepared in a number of different ways we prefer to employ themethods illustrated in the following examples:

Example 1.--Twenty-two grams of alpha amino pyridine and 10.3 grams ofacetaldehyde are mixed and heated together at a temperature of about 50C. for minutes and then cooled. To the resulting liquid mass is thenadded 30 grams of carbon disulfide and the whole heated at about 90 C.for 13 hours. The resulting oily mass is then dried in a vacuum at 90 C.for 100 hours. If desired the dried product may be recrystallized bydissolving it in a srnallamounteothet-lo% sulfuric acid and allowing thesolution to cool. Tfimfistal lized material may then be filtered off anddried as before. The product is a brown amorphous powder, fusing atabout 70 C. It is readily soluble in either warm or cold 5% sulfuricW---- Example 2.--The reaction is carried out in accordance with themethod described in Example 1, using 22 grams of para aminodimethylaniline, 10 grams of acetaldehyde and 30 grams of carbondisulflde. The resulting product in unrecrystallized state is a blackamorphous solid, fusing at about C. and soluble in either warm of cold5% sulfuric acid.

The condensations take place very slowly at room temperatures. Inpractical operation the temperatures employed are limited to a largeextent by the boiling points of the reactants. For example, thecondensation of alpha amino pyridine with acetaldehyde may be carriedout at 35 C. but the reaction requires a great deal of time. At '75 C.the aldehyde may be partly LAQHHHUI lost before it can react.Accordingly, it is preferable to carry out the condensation of thepolyamines with acetaldehyde at temperatures between 40 and 60 C. Wherethe polyamine and the aliphatic aldehyde boil at higher temperatures,the temperature of the condensation reaction may be raisedproportionately. In the condensation with carbon disulfide temperaturesmuch below 75 C. are substantially ineffective and where temperaturesmuch above C. are employed loss of carbon disulfide is likely to result.Therefore, in practical operation, it is preferable to maintain thetemperature of the condensation with carbon disulfide at approximately75 C. to 100 C.

While in the above examples we have disclosed the use of acetaldehyde itis to be understood that aliphatic aldehydes generally may be employed.Some of the aldehydes which have given particularly satisfactory resultsare butyraldehyde, heptaldehyde, crotonaldehyde, and furfuraldehyde.

In the above examples we have illustrated the production of acidinhibitors from alpha amino pyridine and para amino dimethyl aniline,however, it is to be understood that any polyamine having at least oneprimary amino group and one or more tertiary amino groups may besubstituted therefor. Some of the polyamines which we have found toproduce particularly effective acid inhibitors are gamma-aminopyridine,mixed amin'o-pyridines, a,a'-diaminodipyridyl, a-amino-a-picoline,a-amino-lutedine, a-aminouinoline, p-amino-diethylaniline,pamino-methyl-ethylaniline. The various isomers and homologues of thespecifically mentioned polyamines may also be mentioned. Furthermore,mixtures of two or more members of the class may be employed withadvantageous results. Also one or more members of the class admixed witharomatic monoamines such as aniline, the toluidines, dibenzylamine,diphenylamine and phenyl-naphthylamine may be employed to advantage withthe obtention of a composition which is more soluble in dilute acidsthan would be the compounds produced by the use of monoamines only.

The compounds produced as above described are very effective acidinhibitors requiring the addition of only very small amounts thereof toa pickling bath in order to effectively inhibit the solvent action ofthe acid in the bath on the metal, as may be appreciated from thefollowing tests. The efliciency of the products was determined in thefollowing manner.

Small strips of 26 gauge black sheet mild steel, 2 cm. wide and 6 cm.long were superficially oxidized by heating in the flame of a Bunsenburner for a few minutes. These strips were then cooled and weighed andplaced in separate 400 cc. beakers each containing 250 cc. of 5%sulfuric acid at 821-? C. For each test, two strips were employed, onebeing placed in a beaker containing acid to which a small amount of theagent being tested was added, and the other being placed in a beakercontaining acid to which no agent had been added. The beakers containingthe solutions and the metal strips were then maintained at 82:2" C. for30 minutes. At the end of this time all of the oxide scale had beendissolved whereupon the strips were removed, rinsed in water and acetoneand dried. The strips were reweighed and the loss in weight calculated.These losses were of little significance since they included the loss inweight due to removal of scale as well as loss due to removal of metal.The strips were then returned to the beakers from which they were takenand the solutions maintained at 82:2" C. for another hour, the stripswere then removed, rinsed and dried as before. The loss in weight of thestrips due to the one hours immersion in the acid solution was of greatsignificance since such loss represented free metal dissolved in theacid.

In calculating the efficiency of the acid inhibitors from the abovedescribed tests, the loss in weight of the strip in the acid bathcontaining no inhibitor was taken as unity or 100%; the differencebetween such loss and the loss in weight of the strip immersed in acidcontaining acid inhibitor is a measure of the efliciency of theinhibitor used in the second bath. The quotient of the differencebetween the loss in weight of the two strips and the loss in weight ofthe strip which was immersed in acid containing no inhibitor constitutesthe efiiciency or per cent inhibition" of the inhibitor tested, at thetemperature, acid concentration and inhibitor concentration used whenpickling steel of the given composition.

The result of such tests of the compounds whose preparation has beengiven in Examples 1 and 2, computed as above described, is given in thefollowing table:

Table I Concentra- Loss in wt. Percent Agent tion of or metalinhibingent, gms. tion percent None 1 }l.4l0 96.6 96.8 98.9 96. 2 v 297. 5

From the above tests it will be appreciated that the acid inhibitors ofour invention are very effective even at extremely low concentrations.They are also readily soluble in either warm or cold dilute acidsolutions and can be readily rinsed off of the surface of the metal withwater. Their ready solubility makes them very convenient to apply and tohandle and greatly decreases the risks attendant upon the use of thistype of composition. The ease with which they may be removed from thesurface of the metal is of great advantage in cleaning metal forelectroplating, galvanizing and the like.

The pickling solutions prepared in accordance with our invention areparticularly adapted for use in cleaning metal of scale such as occursin welding pipe and the like. They may be used in cleaning pipe andchemical equipment of rust without undue corrosion of the metal and alsofor cleaning metal in preparation for electroplating, galvanizing orlacquering.

While we have disclosed certain specific compounds and a specific methodof producing the same, it is to be understood that such disclosure ismerely by way of illustration and that many modifications and changesmay be made in the compounds, proportions, temperatures, and methodsemployed without departing from the spirit of our invention. Accordinglythe scope of our invention is to be limited solely by the ap- I l 1;mary and at eas Either a ogroupistg':

construed as broadly as is perof the prior art.

amines and aromatic monoamines.

4. A composition of matter useful as an acid inhibitor comprising aproduct obtainable by the chemical combination of an aliphatic aldehydematic monoamine.

5. A pickling solution for metals comprising a strong non-oxidizing acidand a small proportion of a compound obtainable by the combination of an6. A pickling solution for metals comprising a strong non-oxidizing acidand a small proportion of a compound obtainable by the combination of analiphatic aldehyde and carbon disuliide with a diamine in which oneamino group is primary and the other is tertiary.

7. A pickling solution for metals comprising a strong non-oxidizing acidand a small propor- Dyridine nucleus.

8. A pickling solution for metals comprising a strong non-oxidizing acidand a small proportion of a composition obtainable bythe combination ofan aliphatic aldehyde and carbon disulflde with a mixture of an aromaticmonoamine and a diamine in which one amino group is primary and theother amino group is tertiary.

9. The method of cleaning a ferrous metal which comprises treating themetal with a solution containing a strong non-oxidizing acid and acompound obtainable by the combination of an disulfide with a diamine inwhich one amino group is primary and the other is tertiary.

11. The method of cleaning a ferrous metal Examiner which comprisestreating the metal with a solution containing a strong non-oxidizingacid and a composition obtainable by the combination of 13. The methodof cleaning a ferrous metal the metal with a solution containing astrong non-oxidizing acid and a compound obtainable by the chemicalcombination of an aliphatic aldehyde and carbon disulfide with an aminopyridine.

alpha amino pyridine.

16. The method of cleaning a ferrous metal which comprises treating themetal with a solution containing a strong non-oxidizing acid and oneother amino group is tertiary.

20. A composition of matter useful of an aliphatic almixture ofpolyamines and monostrong non-oxidizing acid and a small proportion of acompound obtainable by the combination of carbon disulfide with acondensation product of an aliphatic aldehyde and at least one polyaminehaving at least one primary amino group and at least one tertiary aminogroup.

24. A pickling solution for metals comprising a strong nonoxidizing acidand a small proportion of a compound obtainable by the combination ofcarbon disulfide with a condensation product of an aliphatic aldehydeand a diamine in which one amino group is primary and the other istertiary.

25. A pickling solution for metals comprising a strong nonoxidizing acidand a small proportion of a compound obtainable by the combination orcarbon disulfide with a condensation product of an aliphatic aldehydeand a compound having an amino-pyridine nucleus.

26. A pickling solution for metals comprising a strong nonoxidizing acidand a small proportion of a composition obtainable by the combination ofcarbon disulfide with a condensation product of an aliphatic aldehydeand a mixture of an aromatic monoamine and a diamine in which one aminogroup is primary and the other amino group is tertiary.

2'7. A composition of matter useful as an acid inhibitor comprising aproduct obtainable by the chemical combination of carbon disulfide witha condensation product of acetaldehyde and a mixture of polyamines inwhich at least one of the amino groups is primary and at least one otheramino group is tertiary.

28. A composition of matter useful as an acid inhibitor comprising aproduct obtainable by the chemical combination of carbon disulfide witha condensation product of acetaldehyde and a mixture of polyamines andmonoamines.

29. A composition of matter useful as an acid inhibitor comprising aproduct obtainable by the chemical combination of carbon disulfide witha condensation product of acetaldehyde and a mixture of polyamines andaromatic monoamines.

30. A composition of matter useful as an acid inhibitor comprising aproduct obtainable by the chemical combination of carbon disulfide witha condensation product of acetaldehyde and a mixture of a polyaminehaving at least one primary amino group and at least one tertiary aminogroup and an aromatic monoamine.

31. A pickling solution for metals comprising a strong nonoxidizing acidand a small proportion of a compound obtainable by the combination ofcarbon disulfide with a condensation product of acetaldehyde and atleast one polyamine having at least one primary amino group and at leastone tertiary amino group.

32. A pickling solution for metals comprising a strong nonoxidizing acidand a small proportion of a compound obtainable by the combination ofcarbon disulfide with a condensation product of acetaldehyde a'nd adiamine in which one amino group is primary and the other is tertiary.

33. A pickling solution for metals comprising a strong non-oxidizingacid and a small proportion of a compound obtainable by the combinationof carbon disulfide with a condensation product of acetaldehyde and acompound having an aminopyridine nucleus.

34. A pickling solution for metals comprising a strong nonoxidizing acidand a small proportion of a composition obtainable by the combination ofcarbon disulfide with a condensation product of acetaldehyde and amixture of an aromatic monoamine and a diamine in which one amino groupis primary and the other amino group is tertiary.

35. The mehod of cleaning a ferrous metal which comprises treating themetal with a solution containing a strong nonoxidizing acid and acompound obtainable by the chemical combination of carbon disulfide withthe condensation product of an aliphatic aldehyde and an amino pyridine.

36. The method of cleaning a ferrous metal which comprises treating themetal with a solution containing a strong nonoxidizing acid and acompound obtainable by the chemical combination of carbon disulfide withthe condensation product of an aliphatic aldehyde and an aminodialkylaniline.

37. A'pickling solution for metals comprising a strong non-oxidizingacid and a small proportion of a compound obtainable by the chemicalcombination of carbon disulfide with the condensation product of analiphatic aldehyde and an amino pyridine.

38. A pickling solution for metals comprising a strong non-oxidizingacid and a small proportion of a compound obtainable by the chemicalcombination of carbon disulfide with the condensation product ofacetaldehyde and an amino pyridine.

39. A pickling solution for metals comprising a strong non-oxidizingacid and a small proportion of a compound obtainable by the chemicalcombination of carbon disulfide with the condensation product ofacetaldehyde and alpha amino pyridine.

40. A pickling solution for metals comprising a strong non-oxidizingacid and a small proportion of a compound obtainable by the chemicalcombination of carbon disulfide with the condensation product of analiphatic aldehyde and an amino dialkylaniline.

41. A pickling solution for metals comprising a strong non-oxidizingacid and a small proportion of a compound obtainable by the chemicalcombination of carbon disulfide with the condensation product ofacetaldehyde and an amino dialkylaniline.

42. A pickling solution for metals comprising a strong non-oxidizingacid and a small proportion of a compound obtainable by the chemicalcombination of carbon disulfide with the condensation product of analiphatic aldehyde and an amino dimethylaniline.

43. A pickling solution for metals comprising a strong non-oxidizingacid and a small proportion of a compound obtainable by the chemicalcombination of carbon disulfide with the condensation product ofacetaldehyde and an amino dimethylaniline.

44. A pickling solution for metals comprising a strong non-oxidizingacid and a small proportion of a compound obtainable by the chemicalcombination of carbon disulfide with the condensation product of analiphatic aldehyde and para amino dimethylaniline.

45. A pickling solution for metals comprising a strong non-oxidizingacid and a small proportion of a compound obtainable by the chemicalcombination of carbon disulfide with the condensation product ofacetaldehyde and para amino dimethylaniline.

46. A pickling solution for metals comprising a strong non-oxidizingacid and a small proportion of a compound obtainable by the chemicalcombination of an aliphatic aldehyde and carbon disulfide with a mixtureof polyamines in which at least one of the amino groups is primary andat least one other amino group is tertiary.

4'7. A pickling solution for metals comprising a strong non-oxidizingacid and a small proportion of a compound obtainable by the chemicalcombination of an aliphatic aldehyde and carbon disulfide with a mixtureof polyamines and monoamines.

48. A pickling solution for metals comprising a strong non-oxidizingacid and a small proportion of a compound obtainable by the chemicalcombination of carbon disulfide with a condensation product of analiphatic aldehyde and a mixture of polyamines in which at least one ofthe amino groups is primary and at least one other amino group istertiary.

49. A pickling solution for metals comprising a strong non-oxidizingacid and a small proportion of a compound obtainable by the chemicalcombination of carbon disulfide with a condensation product of analiphatic aldehyde and a mixture of polyamines and aromatic mono-amines.

50. A pickling solution for metals comprising a strong non-oxidizingacid and a small proportion of a compound obtainable by the chemicalcombination of carbon disulfide with a condensation product of analiphatic aldehyde and a mixture of a polyamine having at least oneprimary amino group and at least one tertiary amino group and anaromatic monoamine.

FREDERICK B. DOWNING. RICHARD G. CLARKSON.

